Human heart valves, such as the mitral and tricuspid valves are sometimes damaged by diseases or by aging which cause problems with the proper function of the leaflets and/or the sub-valvular apparatus attached to the leaflets. Often, degenerative disease causes the valve annulus to enlarge to the point where the leaflets attached to it cannot fully close. This inability to completely close, a condition called valve incompetence, eventually requires surgical correction either by valve repair procedures or by valve replacement. In the former, also called valvular annuloplasty, various types of ring-shaped devices or bands fashioned from biocompatible cloth-like materials are sewn to the distended orifice (i.e., annulus of the valve). By properly sizing and devising the annuloplasty ring or band, the surgeon can restore the valve annulus to its normal, undilated, circumference.
Annuloplasty rings or bands are typically of two types, either completely flexible or stiff and comparatively rigid. An example of the former is the Duran Ring or the Cosgrove Band, while an example of the latter is the Carpentier Ring.
The Carpentier Ring consists of a split D-shaped titanium ring completely covered with cloth. The ring is somewhat stiff yet resiliently deformable and is not intended to be removable from the cloth covering. This ring is particularly useful in the repair of heart valves that have lost annular elasticity from, e.g., the chronic effects on the mitral valve of rheumatic fever. Due to their permanent rigidity, the Carpentier Rings lie flat and maintain their D-shape during handling by the surgeon at time of implantation. Many surgeons prefer to use the Carpentier Ring because it is somewhat easier to implant; in particular, easier to achieve a visually aesthetic result with no ring buckling. In addition, it is also easier for the surgeon to test the functionality of the valve immediately after the installation of the repair ring. Although the Carpentier Ring's rigid D-shape is claimed to enhance the competence of the repaired valve, the rigidity also impedes the beneficial flexing movements of the native annulus during the cardiac cycle.
The other major type of annuloplasty ring or band is exemplified by the totally flexible Duran Ring or the Cosgrove Band. These devices consist of a soft core of silicone rubber impregnated with a radiopaque salt (e.g., barium sulfate) completely enclosed by a sheath of biocompatible cloth (e.g., polyester fabric). These devices are completely flexible and useful in the repair of heart valves whose annuli have become enlarged in diameter but are not stiffened and inflexible. Because of its flexibility, the Duran Ring is supported during implantation by a holder which is subsequently removed before tie-off of the sutures, as shown in U.S. Pat. No. 5,011,481 (Myers et al.). One problem with this approach is that the holder does not completely restrain the entire circumference of the ring and does not prevent the flexible ring from bunching or forming pleats as the sutures are tied off. The Cosgrove Band, like the Duran Ring, is totally flexible; however, bunching of the Cosgrove Band is prevented by the mounting of the device on a rigid support, as shown in U.S. Pat. No. 5,041,130 (Cosgrove et al.), which is subsequently removed after the sutures are tied off. Neither the Duran Ring nor the Cosgrove Band can be tested for competence in the ideal systolic shape as can the rigid Carpentier Ring.
Hybrids of the foregoing types of rings have also been proposed, as for example the Sculptor ring in which the anterior segment (which corresponds to the intertrigone area) is rigid but the posterior segment is totally flexible and also fitted with drawstrings to finely adjust its diameter. Although this complex ring can be used in the same circumstances as Duran Ring, it mitigates but does not overcome the handling difficulties associated with flexible rings.
To overcome the deficiencies of the above-described ring/band structures, it would be ideal for an annuloplasty device to be stiff during handling and implantation, but then become flexible after implantation. One such device is disclosed in U.S. Pat. No. 5,716,397 (Myers). In this device, there is a fully flexible annuloplasty ring that is temporarily stiffened during implantation by inserting a withdrawable stiffening wire into a lumen of the ring, which is able to hold the stiffener prior to and during insertion. The stiffening wire includes a portion extending out of the lumen which can be pulled to withdraw it once the device has been implanted. There is still a need, however, for other devices that are generally stiff or rigid during handling and implantation but become more flexible after implantation.
The following documents disclose information about annuloplasty devices.
TABLE 1 ______________________________________ U.S. Pat. No. Inventor Name Date Issued ______________________________________ 5,011,481 Myers et al. April 30, 1991 5,041,130 Cosgrove August 20, 1991 5,716,397 Myers February 10, 1998 5,728,152 Mirsch, II et al. March 17, 1998 ______________________________________ Other Document "Carpentier-Edwards .RTM. Prosthetic Rings Models 4500 adn 4400 for Tricuspid and Mitral Valvuloplasty," Baxter Healthcare Corp., pgs. 1-8 (1/1991). "Cosgrove-Edwards .TM. Annuloplasty System Mitral Model 4600 with Handle/Lanyard for Mitral Valvuloplasty," Baxter Healthcare Corp., pgs. 1-6 (8/1994). "DURAN Flexible Annuloplasty Ring," Medtronic, cover page. "DURAN Flexible Annuloplasty Ring," Medtronic, pgs. 1-8. ______________________________________
All patent and nonpatent documents listed in Table 1 are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate upon reading the Summary of the Invention, Detailed Description of Preferred Embodiments, and Claims set forth below, many of the systems, devices, and methods disclosed in these documents may be modified advantageously by using the teachings of the present invention.